The present invention relates generally to wireless communications, and more particularly to a method for partitioning antenna array in a wireless communication system.
It has become increasingly common for wireless communication systems to equip with a plurality of antennas in order to improve signal coverage and increase system reliability. Beam forming (BF) is one of the transmission schemes that are broadly used, due to its reliability against signal fading. BF is a technique used with arrays of transmitters or receivers that controls a radiation pattern. When receiving a signal, BF can increase the gain in the direction of wanted signals and decrease the gain in the direction of interference and noise. When transmitting a signal, a beamformer controls the amplitude and phase of the signal at each transmitter, in order to create a constructive pattern in a desired direction. As such, information from different sensors can be combined in a way that an expected pattern of radiation can be observed.
Recently, space-time coding (STC) has attracted many attentions in the wireless communication industry. STC relies on transmitting multiple, redundant copies of a data stream to the receiver in order to increase their change of surviving a physical path between transmission and reception, and still remain in a good enough state for reliable decoding. Similar to BF, STC improves reliability against short-term fading.
Depending on various wireless network parameters, it is sometimes advantageous to employ BF and STC simultaneously in an antenna array. This usually requires partitioning the antenna array, where each partition represents a virtual antenna, such that STC can be implemented among various virtual antennas and BF can be performed by each virtual antenna.
FIG. 1 illustrates a conventional antenna partitioning schemes in a wireless communication system, in which both BF and STC are used. At the signal transmitting end, antennas N1, N2 . . . N9 are shown in an array. At the signal receiving end, a wireless node, such as a base station, M1 receives signals from these multiple antennas N1, N2 . . . N9. In this example, antennas N1, N2 and N3 are grouped together in a partition, which is also referred to as a virtual antenna. Likewise, antennas N4, N5 and N6 are grouped together in a separate partition, and antennas N7, N8 and N9 are grouped together in another separate partition. BF and STC are performed using these virtual antennas.
In order to improve the performance of an antenna array implemented with both BF and STC schemes, spatial correlations among these virtual antennas should be low. Besides physical deployments of the antennas, the spatial correlations depend on various factors, mainly the signal propagation environment. Thus, before partitioning an antenna array, its spatial correlations must be obtained through some training, or blind approaches.
Conventionally, it is usually difficult to provide a partitioning scheme, which offers good performance throughout a long time span. This is due to the fact that statistical properties of a wireless channel between an antenna array and a wireless node can change in a way that a partitioning scheme is favorable in a given time and unfavorable in another. For example, with reference to FIG. 2, the properties of a wireless channel between a virtual antenna consisted of antennas N7, N8 and N9 and the wireless node M1 are altered by a bus 200 moving in between them. The bus 200 obstructs signal transmission between the virtual antenna and the wireless node M1, thereby degrading the performance of the partition of antennas N7, N8 and N9.
As such, what is needed is a method for partitioning a plurality of antennas in a wireless communication system using both BC and STC in a way that mitigates the impact a change of channel conditions makes on signal transmission.